1. Field of the Invention
The present invention relates to a heating resistor element, a manufacturing method for the same, a thermal head, and a printer.
2. Description of the Related Art
Conventionally, in a heating resistor element provided in a thermal head of a printer, in order to improve heating efficiency of a heating resistor and to reduce power consumption, a hollow portion is formed in a region opposed to the heating resistor, and the hollow portion is caused to function as a heat insulating layer having low heat conductivity, thereby controlling an amount of heat flowing from the heating resistor to an insulating substrate side (for example, see JP 2007-83532 A).
As a method of forming the hollow portion, there is employed a method of subjecting a silicon substrate to etching or laser processing, and forming a concave portion (having a depth of 1 μm or more and 100 μm or less) to bond thin plate glass (having a thickness of 10 to 100 μm) serving as a heat accumulating layer thereon through anodic bonding performed at a temperature of 700° C. or less. In this case, it is difficult to manufacture or handle the thin plate glass having a thickness of 100 μm or less, and thus thin plate glass having a thickness, which is relatively easily handled, is bonded to a surface of the silicon substrate, and then a surface of a side opposite to a bonded surface is chipped by etching or polishing to obtain a desired thickness size.
In this case, most of the heat generated by the heating resistor is controlled to flow to the insulating substrate side by the hollow portion serving as the heat insulating layer, and is efficiently used as heat for printing. On the other hand, a part of the heat which is not used for printing is transmitted from the heating resistor to a gas contained within the hollow portion through the heat accumulating layer being in contact with the heating resistor, and is further transmitted from the gas contained within the hollow portion to the insulating substrate.
However, in the conventional heating resistor element, the hollow portion is formed by etching or laser processing, and hence a surface of the inner surface of the hollow portion on the insulating substrate side is formed to be extremely smooth, whereby there is an inconvenience that heat of the hollow portion is difficult to be transmitted to the insulating substrate side. That is, heat transmission from the gas contained in the hollow portion to the insulating substrate is performed in a case where gaseous molecules collide against the insulating substrate, but when the surface of the insulating substrate is smooth, the number of the gaseous molecules colliding against the insulating substrate per unit time decreases. For this reason, the heat transmitted to the gas is difficult to be let out to the insulating substrate side, and is accumulated in the gas. Therefore, if the printing is performed for a long period of time, the hollow portion becomes a heat source, which results in a problem of decreased printing quality, such as an occurrence of a tailing phenomenon in which printed characters are connected together in a sheet feeding direction.